A global measure of sickness behaviour: Development of the Sickness Questionnaire

Symptoms after inflammatory activation, so-called sickness behaviour, overlap with trans-diagnostic complaints. As no self-report questionnaire to assess sickness behaviour exists, we aimed to develop such an instrument, the Sickness Questionnaire. Items responsive to experimentally induced inflammatory activation (randomized double-blind study endotoxin (0.6ng/kg) versus placebo, n=52) were selected and the statistical properties were examined in 172 primary care patients. A principal component analysis indicated a one-factor solution (Cronbach's alpha=.86). This 10-item scale correlated with depression (=.41, p<.001), anxiety (=.36, p<.001), self-rated health (=.28, p<.001) and a single item of feeling sick (=.55, p<.001). The results support the adequacy of Sickness Questionnaire as a brief assessment instrument of perceived sickness behaviour.